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Full text of "Text Book Of Mechanical Engineering"

Gun Metal,

to be gone through before the metal is considered fit for the
market.

The metal thus obtained is rolled into plates and hammered
to any shape. Besides its malleability it is exceedingly ductile,
being easily drawn into wires; it becomes brittle if hammered
cold, but its tenacity may be restored by annealing.

Copper is an expensive material, and is only used for pipes
that require bending cold, and for fire-boxes, where ductility as
well as power to conduct and resist heat are needed: it must be
remembered, however, that copper loses its strength somewhat
with increase of temperature.

It is also very useful for electrical purposes, being, next to
silver, the best metallic conductor. (See Appendix If., p* 793.)

(6 and 7.) Zinc and Tin are of little importance singly to the
mechanical engineer.

(8.) Gun Metal is an alloy of Copper and Tin, and is often
called bronze. The proportions are varied for different purposes.

Thus to make 100 parts :—

Copper.

Soft gun metal requires 90
Hard gun metal ,, 82
Bell metal             „ 80

Tin.

I o (General Ordnance purposes.)
18

20

Usually some zinc is added
malleable, as : —

Copper
Tin
Zinc     ,

to   make   the   metal   more

84-22

XO'52

5-26

Gun metal produces fine castings, and being muck stronger
than cast iron, is almost the only other metal preferred
besides cast steel, for the castings required In modern
gunnery. It is often in its harder farm made into bearings
for shafts, Both strength and toughness are increased by rapid
cooling*

(9,) Brass is roMe by alloying wpper with tifa   The pro-